Electrochemical processor

ABSTRACT

An electrochemical processor may include a head having a rotor configured to hold a workpiece, with the head moveable to position the rotor in a vessel. Inner and outer anodes are in inner and outer anolyte chambers within the vessel. An upper cup in the vessel, has a curved upper surface and inner and outer catholyte chambers. A current thief is located adjacent to the curved upper surface. Annular slots in the curved upper curved surface connect into passageways, such as tubes, leading into the outer catholyte chamber. Membranes may separate the inner and outer anolyte chambers from the inner and outer catholyte chambers, respectively.

TECHNICAL FIELD

This application is a Continuation-in-Part of U.S. patent applicationSer. No. 13/110,728 filed May 18, 2011 and now pending, and incorporatedherein by reference.

The field of the invention is chambers, systems, and methods forelectrochemically processing microfeature workpieces having a pluralityof microdevices integrated in and/or on the workpiece. The micro devicescan include submicron features.

BACKGROUND

Microelectronic devices, such as semiconductor devices, imagers, anddisplays, are generally fabricated on and/or in microelectronicworkpieces using several different types of machines. In a typicalfabrication process, one or more layers of conductive materials areformed on a workpiece during deposition steps. The workpieces are thentypically subject to etching and/or polishing procedures (e.g.,planarization) to remove a portion of the deposited conductive layers,to form contacts and/or conductive lines.

Electroplating processors can be used to deposit copper, solder,permalloy, gold, silver, platinum, electrophoretic resist and othermaterials onto workpieces for forming blanket layers or patternedlayers. A typical copper plating process involves depositing a copperseed layer onto the surface of the workpiece using chemical vapordeposition (CVD), physical vapor deposition (PVD), electroless platingprocesses, or other suitable methods. After forming the seed layer, ablanket layer or patterned layer of copper is plated onto the workpieceby applying an appropriate electrical potential between the seed layerand one or more electrodes in the presence of an electroprocessingsolution. The workpiece is then cleaned, etched and/or annealed insubsequent procedures before transferring the workpiece to anotherprocessing machine.

As microelectronic features and components are made ever smaller, thethickness of the of the seed layer deposited into or onto them must alsobe made ever smaller. Electroplating onto thin seed layers presentssubstantial engineering challenges due to the terminal effect. Theterminal effect results due to a large voltage drop across the waferdiameter, caused by the high resistance of the seed layer. If notadequately compensated, the terminal effect causes the electroplatedlayer to be non-uniform, and it may also cause voids within thefeatures. With very thin seed layers, the sheet resistance at the startof the electroplating process may be as high as, for example 50 Ohm/sq,whereas the final sheet resistance of the electroplated film on theworkpiece may be below 0.02 Ohm/sq. With conventional electroplatingtools, this three orders of magnitude change in sheet resistance canmake it difficult or impossible to consistently provide uniformvoid-free films on workpieces. Accordingly, improved electroplatingtools are needed.

SUMMARY OF THE INVENTION

A new processor has now been invented that can successfully electroplatea highly uniform film onto a workpiece, even where the workpiece has ahighly resistive seed layer and/or barrier layer. This new processor mayalso be designed with only two anodes and thief electrode, reducing thecost and complexity of prior designs, while also improving performance.

In one aspect, a processor may include a head having a rotor configuredto hold and make electrical contact with a workpiece, with the headmoveable to position the rotor in a vessel. Inner and outer anodes areassociated with inner and outer anolyte chambers within the vessel. Anupper cup in the vessel, above the outer anode chamber, has a curvedupper surface and inner and outer catholyte chambers. A current thief islocated adjacent to the curved upper surface. Annular slots in thecurved upper curved surface connect into passageways, such as tubes,leading into the outer catholyte chamber. Barriers such as membranes mayseparate the inner and outer anolyte chambers from the inner and outercatholyte chambers, respectively.

Other and further objects and advantages will appear from the followingdescription and drawings which show examples of how this new processormay be designed, along with methods for processing. The inventionresides as well in sub-combinations of the elements described.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, the same element number indicates the same element ineach of the views.

FIG. 1 is a perspective view of a new electro-chemical processor.

FIG. 2 is an exploded perspective view of the processor shown in FIG. 1.

FIG. 3 is a side section view of the processor shown in FIGS. 1 and 2.

FIG. 4 is a front section view of the processor shown in FIGS. 1 and 2.

FIG. 5 is a perspective view cross section of the vessel assembly shownin FIGS. 1-4.

FIG. 6 is an enlarged section view of the vessel assembly.

FIG. 7 is an enlarged rotated section view of the vessel assembly.

FIG. 8A is an enlarged perspective view of the diffuser shown in FIGS. 6and 7.

FIG. 8B is an enlarged section view of an alternative the upper cupshown in FIGS. 5 and 6.

FIG. 8C is an enlarged section view of another alternative upper cup.

FIG. 9 is a top perspective view of the vessel assembly.

FIG. 10 is a schematic perspective view section of the upper cup shownin FIG. 9.

FIG. 10A is a perspective view of an insert for optional use in theprocessor shown in FIG. 10.

FIG. 10B is a graph of a mathematical model of workpiece-to-surface gapvs. radius of a 300 mm diameter workpiece.

FIG. 10C is a schematic representation of a movable vertical edgeshield.

FIG. 10D is a schematic representation of a movable horizontal edgeshield

FIG. 11 is a top view of the upper cup shown in FIG. 10.

FIG. 12 is a catholyte flow path diagram showing the geometry of thecatholyte flow paths in the upper cup shown in FIGS. 10 and 11.

FIG. 13 is another catholyte flow path diagram showing the geometry ofthe catholyte flow paths into the diffuser.

FIG. 14 is a perspective view of a thief ring assembly.

FIG. 15 is an exploded perspective view of the thief ring assembly of.FIG. 14.

FIG. 16 is a section view of the thief ring assembly of FIGS. 14 and 15installed on the vessel 50 as shown in FIG. 9.

FIG. 17 is a section view of an alternative design using a singleelectrolyte.

FIG. 18 is a section view of a modification of the design shown in FIG.8B.

FIG. 19 is a section view of a modification of the design shown in FIG.6.

FIG. 20 is a schematic diagram of a design for changing the effectivelength and resistance of the tubes shown in FIG. 6.

FIG. 21 is a schematic diagram of a ring that be inserted into the lowerends of the tubes or into the slots shown in FIG. 6.

FIG. 22 is an enlarged schematic cross section view of the rings asshown in FIG. 21 installed into the slots shown in FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning now in detail to the drawings, as shown in FIGS. 1-4, anelectro-chemical processor 20 has a head positioned above a vesselassembly 50. The vessel assembly 50 may be supported on deck plate 24and a relief plate 26 attached to a stand 38 or other structure. Asingle processor 20 may be used as a stand alone unit. Alternatively,multiple processors 20 may be provided in arrays, with workpieces loadedand unloaded in and out of the processors by one or more robots. A head30 may be supported on a lift/rotate unit 34, for lifting and invertingthe head to load and unload a workpiece into the head, and for loweringthe head 30 into engagement with the vessel assembly 50 for processing.

As shown in FIGS. 1-3, electrical control and power cables 40 linked tothe lift/rotate unit 34 and to internal head components lead up from theprocessor 20 to facility connections, or to connections withinmulti-processor automated system. A rinse assembly 28 having tiereddrain rings may be provided above the vessel assembly 50. A drain pipe42 connects the rinse assembly 28, if used, to a facility drain. Anoptional lifter 36 may be provided underneath the vessel assembly 50, tosupport the anode cup during changeover of the anodes. Alternatively,the lifter 36 may be used to hold the anode cup up against the rest ofthe vessel assembly 50.

Referring now to FIGS. 3-7, the vessel assembly 50 may include an anodecup 52, a lower membrane support 54, and upper membrane support 56 heldtogether with fasteners 60. Within the anode cup 52, a first or inneranode 70 is positioned near the bottom of an inner anolyte chamber 110.A second or outer anode 72 is positioned near the bottom of an outeranolyte chamber 112 surrounding the inner anolyte chamber 110. The inneranode 70 may be a flat round metal plate, and the outer anode 72 may beflat ring-shaped metal plate, for example, a platinum plated titaniumplate. The inner and outer anolyte chambers may be filled with copperpellets. As shown in FIG. 5, the inner anode 70 is electricallyconnected to a first electrical lead or connector 130 and the outeranode 72 is electrically connected to a separate second electrical leador connector 132. Unlike many earlier known designs, in one embodiment,for example for processing 300 mm diameter wafers, the processor mayhave a center anode, and only a single outer anode, yet still achieveimproved performance due to other design features. Having only twoanodes, instead of three or more anodes, simplifies the design andcontrol of the processor, and also reduces the overall cost andcomplexity of the processor. Designs three or more anodes may alsooptionally be used, especially with even larger wafers.

Turning now to FIGS. 5-9, an upper cup 76 is contained within orsurrounded by an upper cup housing 58. The upper cup housing 58 isattached to and sealed against the upper cup 76. The upper cup 76 has acurved top surface 124 and a central through opening that forms acentral or inner catholyte chamber 120. This chamber 120 is defined bythe generally cylindrical space within a diffuser 74 leading into thebell or horn shaped space defined by the curved upper surface 124 of theupper cup 76. A series of concentric annular slots extend downwardlyfrom the top curved surface 124 of the upper cup 76. An outer catholytechamber 78 formed in the bottom of the upper cup 76 is connected to therings via an array of tubes or other passageways, as further describedbelow with reference to FIGS. 10-12.

Referring still to FIGS. 5-9, the diffuser 74 is positioned within acentral opening of the upper cup 76 and is surrounded by a diffusershroud 82. A first or inner membrane 85 is secured between the upper andlower membrane supports 54 and 56 and separates the inner anolytechamber 110 from the inner catholyte chamber 120. An inner membranesupport 88, which may be provided in the form of radial spokes 114centrally located on the upper membrane support 56, supports the innermembrane 85 from above. This design leaves the inner catholyte chamber120 substantially open, to better allow high current flow from the inneranode to the workpiece while plating onto resistive films. The radialspokes may occupy or block less than about 5%, 10%, 15% or 20% of thecross section area of the inner catholyte chamber 120.

Similarly, a second or outer membrane 86 is secured between the upperand lower membrane supports and separates the outer anolyte chamber 112from the outer catholyte chamber 78. An outer membrane support 89, whichmay be provided in the form of radial legs 116 on the upper membranesupport 56, supports the outer membrane from above.

As shown in FIGS. 5-7, a diffuser circumferential horizontal supply duct84 may be formed in an outer cylindrical wall of the upper cup 76, withthe duct 84 sealed by O-rings or similar elements between the outer wallof the upper cup 76 and the inner cylindrical wall of the upper cuphousing 58. As shown in FIGS. 5, 7 and 8A, radial supply ducts 80 extendradially inwardly from the circumferential duct 84 to an annular shroudplenum 87 surrounding the upper end of the diffuser shroud 82. Theradial ducts 80 pass through the upper cup 76 in between the verticaltubes connecting the annular slots in the curved upper surface 124 ofthe upper cup 76 to the outer catholyte chamber 78. The section view ofFIG. 7 is taken on a plane passing through the radial ducts 80.Consequently, the radial ducts 80 are shown in FIG. 7, while thevertical tubes are not. The section view of FIG. 6 is taken on a planepassing through the vertical tubes. Consequently, the vertical tubes areshown in FIG. 6, while the radial ducts 80 are not.

FIG. 13 shows the circumferential duct 84 and the radial ducts 80leading to the shroud plenum 87, and the outer catholyte paths formedbetween the diffuser shroud 82 and the diffuser 74. These outercatholyte paths are ordinarily filled with liquid catholyte duringoperation of the processor 20. The solid material of the upper cup 76 inwhich these outer catholyte paths are formed, is not shown in FIG. 13.

Turning now to FIGS. 10-12, in the example design shown, there are eightcircumferential slots or rings extending down from the curved uppersurface 124 of the upper cup 76. These are slots 90, 92, 94, 96, 98,100, 102 and 104. The slots are narrow to provide high electricalresistance. The slots are typically between 1 to 5 mm, or 2-4 mm wide.The narrow width of the slots provides for more continuous curved wallshape. When plating workpieces having high sheet resistance, such as 50ohm/square, modeling shows that having a high electrical resistancebetween the anodes and the workpiece, for example greater than 5, 10 or15 ohms, is helpful in achieving uniform deposition. High electricalresistance reduce current leaks down the inner slots and tubes throughthe outer catholyte chamber 78 and up the outer tubes and slots to thewafer edge.

In the design shown, the slots are concentric with each other and withinner catholyte chamber 120. The walls of the slots may be straight,with the slots extending vertically straight down from the curved uppersurface 124 of the upper cup 76. The number of slots used may varydepending on the diameter of the workpiece and other factors. Generallythe slots may extend continuously around the upper cup 76, with nosegmenting or interruptions, and no change in profile or width. However,segmented slots may optionally be used, with the segments at shiftedradial positions, to reduce radial current density variations. Anotheroption for reducing current density variations is to have the radialposition of the slots vary with circumferential angle

As shown in FIG. 10, the outer four slots 104, 102, 100 and 98, in thespecific example shown, are connected into the outer catholyte chamber78 by vertical tubes. The tubes connecting the slots 104, 102, 100 and98 to the outer catholyte chamber 78 are tubes 104A, 102A, 100A and 98A.In the design shown there are 18 tubes connecting into each slot. Thetubes generally are straight wall tubes vertical tubes. The tubes may beuniformly circumferentially spaced apart. The number, size (e.g., crosssection size diameter), length and shape of the tubes may vary to adjustelectrical resistance of the current path through the catholyte in thetubes.

Referring to FIG. 11, in the example shown, the inside diameters of thetubes are greater than the width of the slot that the tube feeds in to.Accordingly, in FIG. 11, the tubes as shown in end view appear morerectangular. A blockage web may also optionally be provided within aslot below the curved upper surface 124 and over the top ends of thetubes, to prevent a direct line-of-sight pathway between the tubes andthe slot. The blockage web, if used, forms an intermediate plenumbetween the tubes and the slot.

Keeping in mind that FIG. 10 shows the open catholyte chambers andpathways, and not the surrounding solid material forming these chambersand pathways, the upper cup 76 may be formed of a di-electric material,such as Teflon (fluoro-polymer) or natural polypropylene, optionallywith a two-piece assembly.

In the design shown having 18 tubes (i.e., vertical bores or throughholes in the upper cup 76) there is a 20 degree spacing between thetubes. If the number of tubes is reduced, the resistance in each ring oftubes increases significantly, which enables the tubes be made shorter.Although FIG. 11 shows the tubes in each of the rings of tubes asradially aligned, the tubes in any ring of tubes may alternatively bestaggered from the tubes in an adjacent ring of tubes.

Electrical current density uniformity at the slot exit is most heavilyinfluenced by the height of the slots and the pitch of the tubes. Aspectratios of slot height/tube pitch greater than 1.0 generally arepredicted to provide good current density uniformity. Tube insidediameters may range from about 3-12 mm or 5-7 mm. A combination of a 2-5mm slot width and 4-8 mm tube diameter may be used.

In an alternative design, the slots 94-104 (or however many slots areused) have a very narrow width, for example 1 mm, and extend entirelythrough the upper cup 76, from the curved upper surface 124 of the uppercup 76 to the outer catholyte chamber 78. In this design no tubes areused or needed. Rather, the very narrow slots provide a sufficientlyresistive path, without the use of discrete tubes. As forming slots onlye.g., 1 mm wide may not necessarily be easily achieved (due to limits onmachining or forming techniques), the tubes may be preferred over use ofnarrow full-length slots. Since the tubes provide discrete spaced apartopenings, in comparison to the continuous opening in a slot, rotation ofthe workpiece may be used with processors using tubes to average outcircumferential variations caused by the spaced apart discrete tubeopenings.

Referring still to FIG. 10, slots 96 and 94 may be closely spacedtogether with a single set of tubes 96A connecting into both of theseslots. Similarly, slots 92 and 90 may be closely spaced together with asingle set of tubes 92A connecting into these slots. The length of thetubes is selected to adjust electrical resistance through the catholytecontained by the upper cup 76. As shown in FIG. 10, the top end of eachof the tubes, where the tubes join into the slots, may be at the samevertical position VP. However, the vertical position of bottom ends ofthe tubes may be varied changing the length of the tubes. This may beachieved via steps formed in the bottom surface of the upper cup 76. Thesteps shown in FIG. 10 are steps 92B, 96B, 98B, 100B, 102B and 104B,with the element number of each of the steps associated with thecorresponding element number of the tubes and the slots. For example,the outermost slot 104 is connected to tubes 104A which connect to step104B. Steps 104B and 102B may be at the same vertical position, withsteps 100B, 98B and 96B progressively rising, and with step 92B lowerthan step 96B, and at about the same vertical position as step 98B.

Flexibility in adapting the slot height and tube spacing (pitch) to aspecific process can be advantageous, especially with copper damasceneprocesses, which are sensitive to circumferential variations in currentdensity, even when time-averaged by rotating the workpiece. Use of thesteps to independently adjust the lengths of the tubes in each ring oftubes can help improve the radial current density profile.Correspondingly, step inserts 106 or insert rings, such as shown in FIG.10A, may be provided as replaceable components that can be selected andinstalled into the processor below the tubes to change the effectivelength of the tubes. Use of the inserts 106 may be helpful duringinitial set up or dialing in of the processor, as the inserts willchange the relative amount of electrical current passing through eachslot when setting up the processor for a particular process.

The effective length of the tubes may alternatively be selected byvarying the vertical position of the bottom of each of the slots, withor without using steps of any similar element. FIG. 12 is a perspectivesimilar to FIG. 13 described above in the sense that it shows the outercatholyte spaces of the liquid catholyte through the diffuser and theupper cup 76, rather than the solid material of these elements. Forclarity of illustration the outer catholyte spaces in FIG. 12 have thesame element numbers as the features or elements that form or define theouter catholyte spaces. Although described in terms of tubes and steps,generally, depending on the manufacturing technique used, the tubes maybe formed as holes through the material forming the upper cup 76, andthe steps may similarly be formed as rectangular cross section ringsformed in the bottom of the upper cup 76.

FIG. 10B shows an analytical model of a curvature of the upper surface124 of the upper cup 76. The curves for a 108 mS/cm, 50 Ohm/Sq and a 250mS/cm, 20 ohm/sq overlie each other. The lower curve is for a 108 mS/cm,20 Ohm/sq model. Note that the shape of the curve also depends upon theassumed gap between the wafer edge and the cup. Since the curves dropaway from center of the wafer moving outwardly towards the wafer edge tothe wafer center, the design of the upper cup 76 is consistent with theflow of catholyte. The two chamber wall curves in FIG. 10B that nearlyoverlay each other do so because they are for cases that compensate forabout the same wafer terminal effect. The terminal effect isproportional to the ratio of the film sheet resistance divided by thebath resistance (i.e. the inverse of the bath conductivity). Therefore,a smaller seed layer sheet resistance using a high conductivity bath (20Ohms/sq with 250 mS/cm) will yield a similar terminal effect for ahigher sheet resistance in a lower bath conductivity (50 Ohms/sq with108 mS/cm).

The so-called terminal effect causes a higher deposition rate at theedge of the workpiece relative to the center. Accordingly, if notcompensated, the terminal effect will result in non-uniform plated filmsor layers on the workpiece. To better compensate or control the terminaleffect, at the outset of plating, the head may hold the workpiece at afirst position relatively close to the surface 124 of the upper cup.Then, as film thickness on the workpiece increases and the terminaleffect decreases, the head may lift the workpiece to a second positionfurther away from the surface 124, to better avoid uneven depositionresulting from the proximity of the workpiece to the circumferentialslots 92-104 in the upper cup. This change in spacing however can resultin edge effect deviations in the electric current density around theedges of the workpiece.

FIG. 10C shows an example of a vertical edge shield 128 that may be usedto compensate for these current density variations. The edge of theworkpiece is shown at 191. The edge shield 128, typically made of adi-electric material, may drop into an opening below the surface 124during the initial plating, when the film resistance is high, and thenrise up out of the opening, to the position shown in FIG. 10C, as theworkpiece is moved away from the surface 124 during later plating. Theshield 128 may be moved by an actuator 129.

FIG. 10D shows a horizontal edge shield 190 (in white) with thecatholyte shown in gray. The workpiece edge is shown at 191. The shield190 may be formed with a horizontal ring 192 joined to a verticalannular ring 194. Alternatively, the horizontal ring 192 may be usedalone and supported on spacers. Alternatively, the horizontal ring 192may be supported on springs in the upper cup. In this design, as theworkpiece is moved up away from the upper cup, the springs lift theshield 190 (or 128) to a raised position. When the workpiece is in theinitial lower position closer to the upper cup, the rotor holding theworkpiece holds the shield down into a recess in the upper cup. Thehorizontal ring 192 may be positioned in recess or groove around theperimeter of the upper cup. In comparison to the design in FIG. 10C, inthe design in FIG. 10D, the horizontal orientation of the ring 192allows the thief current to pass over the entire height of the gapbetween the curved wall and the workpiece, above and below vertical ring194. The horizontal ring 194 further restricts the current flow path tohelp adjust the amount of thief current that passes above or below thehorizontal ring 192. While the shield 128 in FIG. 10C controls thecurrent crowding to the edge of the wafer, all thief current is alsoconcentrated there to flow above shield 128 to a smaller gap between thetop of 128 and the wafer. The enhanced influence on the current thief atthe edge of the workpiece in this design may be moderated with changesin other design parameters.

FIG. 9 shows the outside of the processor 20 and the connections orfittings for providing process fluids into and out of the processor 20.Referring to FIGS. 6 and 9, anolyte is provided into the inner anolytechamber 110 via inlet 154. Anolyte is provided into the outer anolytechamber 112 via inlet 148. Fitting 146 is an anolyte idle staterecirculation port for the outer anolyte chamber 112. Fitting 150 is anouter anolyte chamber 112 return/refresh port. Fitting 156 is an inneranolyte chamber return/refresh port. As shown in FIG. 6, anolyte flowsout of the inner anolyte chamber via a circulation slot 162, and anolyteflows out of the outer anolyte chamber via a circulation slot 160.During idle state, when the processor contains anolyte but is notactively processing, outlet 152 allows anolyte to outer catholyte out ofthe processor. This drops the anolyte level so that the anolyte is notin contact with the membranes, to better avoid diffusion of componentsof the catholyte and anolyte.

Referring to FIGS. 5 and 9, catholyte flows up and radially outwardly inthe inner catholyte chamber 120 and is collected in a collection ringchamber 122. Catholyte flows out of the collection ring chamber 122 to areturn port 158 for recirculation. A catholyte level indicator 140monitors the catholyte liquid leveling the upper cup 76. The termsanolyte and catholyte as used here refer to the location of theelectrolyte in the processor, and not necessarily to any specificchemical make up of the electrolyte. The indicator 140 may be connectedto a computer controller controlling the processor, or an array ofprocessors in an automated system. A computer controller may also beused to control various other parameters in the operation of theprocessor 20. Excess catholyte flows out of the processor via acatholyte drain 142 shown in FIG. 9.

As shown in FIGS. 2, 3 and 4, a rotor 180 in the head 30 is rotated by amotor 184. The rotor 180 is adapted to hold a workpiece or wafer. Acontact ring on the rotor makes electrical contact with the workpiece. Anozzle 186 may be provided in the head 30 centrally aligned over theworkpiece holding position of the rotor 180. Representative rotors 180are described in U.S. Pat. Nos. 6,527,926, 6,699,373 and 7,118,658,incorporated herein by reference.

FIGS. 14, 15 and 16 show a current thief electrode assembly 200 that maybe used with the processor 20. The assembly 200 includes a ring 202attached to a housing 204. A wire 208, such as a platinum wire, extendsthrough a membrane tube 206 positioned within a groove 216 in the ring202. The ends of the wire 208 terminate within the housing 204 and areconnected to a voltage source via a connector 210. Electrolyte is pumpedthrough the membrane tube 206 via an inlet fitting 212 and an outletfitting 214 attached to the housing 204. The electrolyte liquid providedto the thief assembly 200 (“thiefolyte”) may be different from catholyteliquid provided into the upper cup 76. As shown in FIGS. 9 and 16, theassembly 200 fits on top of the upper cup 76 and may be used to changethe electrical current flow characteristics of the processor 20. Theassembly 200 may be quickly and easily removed from the upper cup 76 andreplaced, as a unit. Designs such as described in U.S. Pat. No.7,727,364, incorporated by reference, may also be used.

In use, a workpiece, typically having an electrically conductive seedlayer, is loaded into the head. The seed layer on the workpiece isconnected to an electrical supply source, typically to the cathode. Ifthe head is loaded in a face up position, the head is flipped over sothat the rotor, and the workpiece held in the rotor, are facing down.The head is then lowered onto the vessel until the workpiece is incontact with the catholyte in the vessel. The spacing between theworkpiece and the curved upper surface 124 of the upper cup 76influences the current density uniformity at the workpiece surface.Generally, the workpiece-to-surface gap (the least dimension between anyportion of the curved upper surface 124 and the workpiece) is about 4-14mm. This gap may be changed during processing. The workpiece may bemoved up and away from the surface 124 gradually, or it may be movedquickly from a starting gap to an ending gap. A lift/rotate mechanismsuch as described in U.S. Pat. No. 6,168,695, incorporated herein byreference, may be used to lift the head.

Anolyte is provided into the inner anolyte chamber 110 and separatelyinto the outer anolyte chamber 112. Catholyte is provided into thecircumferential supply duct 84. Thiefolyte is supplied to the inletfitting 212. The workpiece is moved into contact with the catholyte,typically by lowering the head. Electrical current to the anodes 70 and72 is switched on with current flowing from the anodes through theanolyte in the inner and outer anolyte chambers 110 and 112. The anolyteitself flows as shown by the dotted arrows in FIG. 6. The electricalcurrent from the inner and outer anodes passes through the anolyte andthrough the inner and outer membranes 85 and 86, respectively, and intothe catholyte contained in the open spaces in the upper cup 76.

Within the upper cup 76, catholyte flows from the supply duct 84radially inwardly, to the diffuser shroud plenum 87 and then into thediffuser 74 as shown via the arrows in FIG. 8A. The catholyte flows upfrom the diffuser and moves radially outwardly in all directions overthe curved upper surface 124 of the upper cup 76. Metal ions in thecatholyte deposit onto the workpiece, building up a metal layer on theworkpiece. The motor 184 may be switched on to rotate the rotor 180 andthe workpiece, to provide more uniform deposition onto the workpiece.Most of the catholyte then flows into the collection ring 122. A smallfraction of the catholyte flows downwardly through the slots 90-104 andthe tubes 92A-104A into the outer catholyte chamber 78. The catholytethen flows out of the processor 20.

Generally in electrochemical processors, electrical current tends toflow through all available pathways, resulting in so-called currentleaks caused by voltage gradients with the reactor. Current may leakbetween anode channels through paths such as a membrane or ventholes/slots. Current may also leak along walls of processor components,such as a diffuser. This can cause current density variations at theworkpiece surface, resulting in varying deposition rates and ultimatelya plated-on metal layer having unacceptable variations in thicknessacross the workpiece, especially in copper damascene applications.Voltage gradients within the reactor can be particularly large at thebeginning and end of plating. When plating on a highly resistive seedlayer, current flow is mainly between the inner anode 70 and both theworkpiece and the current thief. As a result, the voltage in the inneranode cup and membrane chamber can be quite high (over 100 Volts) whilethe voltage within the outer anode chamber is low. This large voltagedifference can result in significant current leaks, even via relativelysmall current leak paths. Accordingly, use of separate, individuallysealed inner and outer current paths improves the processor performancewhen plating onto thin seed layers. This includes use of separateindividually sealed membranes. The situation can be reversed whenplating onto thick, low resistive films when the bulk of the current isfrom the outer anode. Then, a similarly large, but opposite voltagedifference can again exist between the inner and outer anode channels orcurrent paths.

Referring to FIG. 5, the processor may be described as having inner andouter current channels. Using this description, the inner currentchannel extends generally vertically up from the inner anode 70, throughthe inner membrane 85, the diffuser 74, and the central catholytechamber 124 to the workpiece. The inner current channel may bevisualized substantially as a cylindrical tube. The outer currentchannel may correspondingly be visualized as extending vertically upfrom the outer anode 72, through the outer membrane 86, the outercatholyte chamber 78, and through the openings in the upper cup to theworkpiece. The inner and outer current channels are advantageouslysealed and isolated from each other by seal elements such as O-rings andwalls of dielectric material, to reduce current leakage between them.

The tubes and slots within upper cup 76 are designed to reduceelectrical current leakage into and out of the outer anode chamber. Inorder to plate uniformly on a resistive seed layer, a large radialvoltage gradient is necessarily generated within the metal film. Theprocessor must match this radial voltage gradient within the catholyte.So, a large voltage gradient will exist along the surface of the curvedchamber wall from the center to the edge (driven by the current betweenthe inner anode and both the wafer and the thief). The voltage at theslots 90, 92, 94, and 96 in the curved chamber wall will be highervoltage than at the slots 98, 100, 102, and 104 which are farther fromthe center. Therefore, a leakage current flows into the inner slots andthen back out of the slots closer to the edge of the wafer. This currentpath is undesirable leakage because is bypasses the intended currentpath through the fluid path along the curved chamber wall and decreasesthe radial current density uniformity across the wafer. To minimize theamount of current though this leakage path, the resistance of the pathis made very large by using relatively few and long holes 90A, 92A, 94A,96A,98A, 100A, 102A, 104A. At the same time, the relative resistancethese rows of holes is set, not for current leakage concerns, but toassure the proper radial current distribution from the outer anode 2 tothe wafer. The resistance of each row of holes (each radial circle) maybe greater than 5 Ohms and more specifically approximately 10 Ohms. Thechoice of the slot widths is related to the current gradient that existsalong the curved when plating on a resistive seed layer. Wide slotsdistort the curved wall and can be detrimental to the radial currentdensity distribution across the wafer. Wide slots allow the current todip into and out of a slot as it travels along the wall. However, theslot width is a trade-off because a wider slot is beneficial at the endof plating on a blanket film to avoid deposition bumps that can beproduced on the wafer under each slot.

As shown in FIG. 11, the outer slots 100, 102 and 104 may be spaced moreclosely together than the inner slots 90, 92, 94, 96 and 98. Generally,the closer the slots are to the workpiece, the closer the slots may betogether, to better reduce current variations at the workpiece surface.

Electrical potential may also be applied to the thief electrode such asthe wire 208, adjacent to the edges of the workpiece, to achieve a moreuniform deposition of metal on the workpiece. As shown in FIG. 16, thewire 208 of the thief assembly 200 is positioned within the membranetube 206 at or near the bottom of the groove 216. The open top 218 ofthe groove 216 acts as a virtual electrode, as described for example inU.S. Pat. No. 7,842,173 B2, incorporated herein by reference. As theterminal effect decreases as the electroplating process proceeds and thesheet resistance of the workpiece drops, the thief current may also bereduced.

The rotor 180 may use a sealed contact ring or it may use a wet orunsealed contact ring. If a sealed contact ring is used, the sealgenerally distorts the electric field near the edge of the workpiece.However, this distortion may be compensated, at least in part, via thedesign of the upper cup 76. The outer perimeter of curved upper surface124 of the upper cup 76 beyond the outermost slot (slot 104 in thedesign shown) may be designed to rise up to the seal. This upwardlyextending outer area of the upper surface 124 of the upper cup 76 may becurved or flat. The upwardly rising outer perimeter of the upper cup 76forces the thief current to pass through a narrow gap close to the seal.

The electric field distortion associated with use of a sealed contactring may also be reduced via the design of the ring 202 of the thiefassembly 200. As shown in FIG. 16, the inner edge 215 of the ring 202provides a step up from outer edge of the top surface 124 of the uppercup. The step height may be about 2-6 mm. The ring 202 may be quicklyand easily installed or removed since it is part of the modular thiefelectrode assembly 200. The processor 20 may be provided with a singleupper cup fixed in place, with the ring 202 of the thief assemblyselected based on whether a sealed or un-sealed contact ring is used.

A method for electrochemically processing a wafer or workpiece includesholding the workpiece in a head, with the head lowering the workpieceinto contact with catholyte in a vessel. Electrical current is suppliedto an inner anode associated with an inner anolyte chamber within thevessel, and to an outer anode surrounding the inner anode, the outeranode associated with outer anolyte chamber. Electrical current flowsthrough catholyte in annular slots in an upper curved surface of anupper cup in the vessel. Electrical current also flows from a currentthief adjacent to upper curved surface of the upper cup. Catholyte flowsupwardly towards the workpiece from an inner catholyte chamber separatedfrom the inner anolyte chamber via a membrane. Catholyte may also flowdownwardly through the slots into an outer catholyte chamber.

The workpiece may optionally be rotated. The workpiece may also belifted up and away from the upper curved surface of the upper cup duringprocessing, with the lifting rate a function of the film sheetresistance on the workpiece. The electrical resistance in the currentpath between the anodes and the workpiece may be greater than 5, 10 or15 ohms.

For some applications, especially with large diameter workpieces, theprocessor 20 may be modified to include more than one outer anode.

As shown in dotted lines in FIG. 8A, a center catholyte jet 228 may beprovided to increase the mass transfer rate at the central area of theworkpiece. The catholyte jet 228 may be formed by a center jet opening230 in the inner membrane support 88. A duct 232 in one or more of thespokes 114 of the inner membrane support may supply catholyte to thecenter jet opening 230.

As shown in FIG. 8B, in an alternative upper cup 76A, the top surfaces240 of the outer catholyte chamber 78 are slanted up towards the outerwall. In comparison to the flat or horizontal surfaces shown in FIGS. 5and 6, the design in FIG. 8B is less prone to trap air bubbles in thecatholyte. The inclined surfaces 240 in FIG. 8B tend to convey anybubbles in the catholyte chamber up and radially out towards a recess242 and a vent 244. The lower openings of the tubes are at differentvertical positions. The tube diameters and the slot lengths may beadjusted to achieve appropriate electrical resistance.

As shown in FIG. 8C, in another alternative upper cup design, each tubeextending up from the outer catholyte chamber 78 transitions into twoslots opening in the curved upper surface 124 of the upper cup. Theupper cup in this design has 12 slots. Also as shown in FIG. 8C, theinner top surface 250 of the outer catholyte chamber slopes upwardly,and the outer top surface 252 slopes downwardly (moving radiallyoutwardly), with an abrupt step down 254 between them. This alternativedesign of the top surfaces of the outer catholyte chamber may alsooptionally be used to reduce or avoid trapping air bubbles.

FIG. 17 shows an alternative processor 260 similar to the processor 20shown in FIGS. 1-7 but using a single electrolyte. The processor 260 hasno membranes or other barrier separating lower and upper chambers.Rather, the inner and outer flow channels extend up from the anodesthrough the upper cup. Electrolyte enters via the supply duct 84 (andwith the inner channel filled with electrolyte), flows up and radiallyoutwardly, and over the weir, with a small fraction of the electrolyteflowing down through the slots and tubes (similar to the catholyte inthe processor 20). However, since there are no separate upper and lowerchambers, the electrolyte flowing down through the tubes flows into theanode compartments, and then out of the processor 260 via outlets 262and 266. Since the processor 260 has no membranes, no membrane supportsare needed.

The processor 20 can plate with uniform current density onto asemiconductor or other work piece over a broad range of metal film sheetresistances, including very high sheet resistance seed layers having asheet resistance of 50 Ohms/sq or more. This capability is becomingincreasingly significant, especially as to copper damascene films, asfeature sizes get smaller and smaller. During the plating process, thesheet resistance of the metal film on the wafer changes from a very highinitial resistance, for example 50 Ohm/sq or higher, to a much lowersheet resistance of, for example, 0.02 Ohm/sq, as metal is deposited andthe metal film thickness increases. Controlling the electric field inthe processor as this occurs, to maintain uniform plating, presentsengineering challenges.

The curved top surface 124 of the upper cup 76 performs very well forplating onto an initial very thin-seed layer, typically when only theinner anode 70 and the thief assembly 174 are used, and the second anode72 is substantially off. As the thickness of the plated metal filmgrows, and the sheet resistance decreases, the second anode 72 is usedto help to control the electric field. Slots, such as the slots 90-104are provided in the upper cup 76 to allow current from the second anode72 to help control the electric field. However, it has been discoveredthat the slots may also alter the ideal performance of the curvedsurface 124 on the thin seed layer, primarily due to current leakagethrough the second anode 72 current pathways.

Although the second anode current pathways have high resistance, somecurrent from the inner anode 70 still flows through them during platingof the very thin initial seed layer. This changes the electric field inthe processor 20, making it less effective at uniformly plating onto theinitial seed layer. Specifically, some current from the first anode 70flows down through inner slots and tubes into the analyte reflow chamber78, and then up through outer tubes and slots to the edge of the wafer.The result may be that this current leakage causes the current densitytowards the edge of the wafer to be too high and the current densityaway from the edge to be too low, for uniform plating.

The current leakage may be reduced by increasing the resistance of thetubes connecting the slots. However, this also increases the cellvoltage and the power supply requirements. To control current leakagewithout increasing the power supply requirements, electrical pathwayswithin the processor may be physically changed via mechanical elements.Specifically the effective length and/or diameter of the tubes may bechanged, correspondingly changing the electrical resistance of the flowpaths through the tubes. During initial plating, the tubes may be set tomaximize resistance, thereby minimizing current leakage through them.After the initial plating, the resistance of the tubes may be reduced toallow passage of more current from the second anode, without placingexcessive power requirements on the processor power supply.

FIG. 18 shows one technique for mechanically changing the resistance ofthe current path through the tubes. In this technique, a modified uppercup 270 has a truncated cone or conical section plate 272 at the bottomopenings of the tubes. The plate 272 has holes or slots aligned with thetubes. A plate actuator 274 is linked to the plate 272 for rotating theplate slightly, from a fully closed position where the plate 272entirely blocks off the lower ends of the tubes, to a fully openposition, where the holes in the plate 272 are fully aligned with thetubes. With this design, some or all of the tubes 92A, 96A, 98A, 100A,102A and/or 104A may be closed off during initial plating of the thinseed layer. Via control of the plate actuator 274, the tubes may then beopened partially or fully as the sheet resistance of the waferdecreases. The plate 272 may also be designed to allow a differentradial current distribution at different rotational positions.

The plate actuator 274 may be a two position actuator, such as apneumatic actuator, that moves the plate 272 into either a fully open orfully closed position. Alternatively, the plate actuator 274 may beanother type of actuator, such as an electrical actuator, that can movethe plate 272 continuously, and select any position ranging from fullyopen to fully closed. The plate actuator 274 may be linked to the plate272 via a mechanical linkage, or via a magnetic or electromagneticcoupling. Although FIG. 18 shows the plate 272 as a conical section, forprocessors having flat top surfaces 240 in the analyte reflow chamber78, a flat plate 272 may be used.

For some applications, the plate may also be set and left at a desiredposition and not changed during the plating process. For example, if theprocessor 20 will be processing wafers having a thick seed layer, theplate 272 may be left in the fully open position throughout the platingprocess.

FIG. 19 shows another design which allows the resistance of the tubes tobe changed. In this design, an upper cup 280 includes tube extensions282 that can slide or telescope into and out of the tubes 92A, 96A, 98A,100A, 102A and/or 104A. The tube extensions 282 may be attached to abridging ring or plate 290. A plate actuator 292 moves the bridgingplate 290 up or down, to effectively change the length of the tubes,thereby changing the electrical resistance of the current path throughthe electrolyte in the tubes. The design and operation of the actuator292 may be the same as the actuator 274 discussed above. The tubelengths may also be adjusted within each ring using the tube extensions282, to tune the radial electrical current distribution to the wafer.

FIG. 20 shows another design for changing the effective length andresistance of the tubes using a threaded tube insert 320. An uppersegment 322 is attached to a lower segment 324 via screw threads 366. Athreaded tube insert 320 may be placed into some or all of the tubes92A, 96A, 98A, 100A, 102A and/or 104A. Turning the lower segment 324relative to the upper segment 322 lengthens or shortens the effectivelength of the tubes. The tube lengths in FIG. 20 may similarly beadjusted to control the radial electrical current distribution to thewafer.

FIGS. 21 and 22 show another processor design 300 with rings 302designed to fit into one or more of the slots 90, 92, 94, 96, 98, 100,102 or 104. The rings 302 may be dimensioned so that they may be pressedinto the slots. The rings 302 may have through holes 310 aligned overthe tubes, with the hole diameters selected to change the effectiveresistance of the tubes. Some of the hole positions may be omitted orclosed with a permanent or temporary plug 312. The hole diameters mayall be the same or they may be different. As shown in FIG. 22, the rings302 may alternatively have posts 306 that extend partially into thetubes, with the diameter of the post less than the tube diameter, toallow for limited current flow through the tube. The rings 302 may bemade of an anisotropic material, such as a ceramic having a high densityof holes or slots, to reduce current leakage pathways. One example ofthis design is an alumina plate with a pattern of small diameterparallel through holes.

As shown in FIG. 22, the rings 302, if used, may be placed into theslots from above. Consequently, the rings 302 may be installed andremoved without dismantling the processor 20. The rings 302 may be usedto partially or fully block flow of electrical current through theslots, to adjust the radial distribution of the electrical current.Rings as shown in FIG. 21 may alternatively be inserted into the lowerends of the tubes 92A-104A. Referring still to FIG. 22, the bottomsurfaces of the rings 302 may be flat or angled, and the relative heightof each ring, from the bottom surface to the top surface, may vary fromslot to slot to help adjust the relative resistance if using ananisotropic material.

The upper cups 76 described above may be made of plastic, ceramic, orother dielectric materials. For processors designed for handling largersize wafers, such as 450 mm diameter, ceramic materials may be used tobetter stay within dimensional design tolerances. As shown in FIG. 8A,radial branch slots 108 may branch out of a middle area of the innerslot 90 into the surface 124 of the upper cup 76, adjacent to thediffuser 74. The radial branch slots 108 may be interrupted orcontinuous, with FIG. 8A showing interrupted radial branch slots.Although the surface 124 is described here as a curved surface, it mayoptionally approximate a curve using multiple incremental steps of thesame or varying length, in a stairway type of design.

Thus, novel processing apparatus and methods have been shown anddescribed. Various changes and substitutions may of course be madewithout departing from the spirit and scope of the invention. Theinvention, therefore, should not be limited except by the followingclaims and their equivalents.

1. A processor comprising: a vessel; a head configured to hold aworkpiece, with the head moveable to position the workpiece in thevessel; an inner anode associated with an inner anolyte chamber withinthe vessel; an outer anode surrounding the inner anode, the outer anodeassociated with an outer anolyte chamber; an upper cup in the vesselhaving an upper curved surface, an outer catholyte chamber over theouter anolyte chamber, and an inner catholyte chamber over the inneranolyte chamber; a plurality of openings in the upper curved surface ofthe upper cup; a passageway connecting substantially each of theopenings to the outer catholyte chamber; and an adjusting elementassociated with the passageways movable between a first position wherethe passageways are un-occluded to a second position where thepassageways are at least partially occluded.
 2. The processor of claim 1wherein the adjusting element comprises a plate having a pattern ofthrough openings in a pattern matching the passageways.
 3. The processorof claim 2 wherein the plate is conical.
 4. The processor of claim 2further comprising an actuator attached to the plate for moving theplate between the first and second positions.
 5. The processor of claim1 with the adjusting element in the inner catholyte chamber.
 6. Aprocessor comprising: a vessel; a wafer holder moveable to position aworkpiece in the vessel and to make electrical contact with a downfacing surface of the wafer; an inner anode associated with an inneranode channel within the vessel; an outer anode surrounding the inneranode, the outer anode associated with outer anode channel, with theouter anode channel substantially electrically isolated from the inneranode channel by dielectric material walls and seals; an upper cup inthe vessel having an upper curved surface; a plurality of annular slotsin the upper curved surface of the upper cup; a plurality of passagewaysconnecting substantially each annular slot to the outer catholytechamber; and a passageway adjuster associated with at least some of thepassageways for adjusting the length of the passageways.
 7. Theprocessor of claim 6 with the passageway adjusters comprise tubesextending out of the passageways.
 8. The processor of claim 7 with thetubes attached to a ring, and further comprising a ring actuator forchanging the positions of the tubes relative to the openings.
 9. Aprocessor comprising: a vessel; an inner anode associated with an innerelectrolyte channel within the vessel; an outer anode surrounding theinner anode, the outer anode associated with an outer electrolytechannel within the vessel; an upper cup in the vessel having an uppercurved surface; a plurality of concentric slots in the upper curvedsurface of the upper cup; a tube extending substantially from each ofthe slots to a lower surface of the upper cup; and a ring insert in oneor more of the slots.
 10. The processor of claim 9 with the ringcomprising an anisotropic material.
 11. The processor of claim 9 withthe ring having a plurality of openings aligned over the tubes.
 12. Theprocessor of claim 9 with the ring having an angled bottom surface.